The invention relates to an improved medical fluid flow set and method of manufacturing the same. Particularly, the invention may be used as arterial hemodialysis sets which carry a negative pressure pillow, as is customary in commercial embodiments of such sets.
Arterial sets are used in conjunction with hemodialyzers to convey blood from the patient to the hemodialyzer, where metabolic waste products such as urea, water, and creatinine are removed. Then, the blood flows from the hemodialyzer via a venous hemodialysis set back to the vein of the patient.
Conventionally, arterial sets for hemodialysis contain a negative pressure pillow, which pillow constitutes a small enlargement of the flow tubing of the arterial set, positioned in-line intermediate the ends of the set tubing. Typically, the pillow is of a wall thickness which is thick enough to at least partially collapse when predetermined negative pressure conditions are encountered in the arterial set. A branch line typically extends laterally outwardly from the conventional negative pressure pillow, to connect to a source of saline solution or the like for use in priming of the set, and also for rinsing back the blood from the set to the patient to minimize the loss of blood experienced by the patient during a hemodialysis procedure.
The collapse of the pillow at a certain negative pressure typically activates a microswitch with which the pillow is placed in contact, to stop or reduce blood pump speed until sufficient arterial set pressure is restored. It is to be understood that the term "negative pressure" is commonly used among those skilled in the art, and relates to a pressure which is less than atmospheric.
By the above means, it is assured that the hemodialysis system will not run dry of blood because of excessive roller pump speed, outpumping the capacity of the arterial set to draw blood from the patient.
Alternatively, a physiologic fluid source such as saline solution can be administered through the branch tube of the pillow instead of, or in addition to, slowing or stopping of the pump, in order to restore desired fluid pressure in the arterial set. This pillow is also typically placed in engagement with a microswitch, but it operates as part of an apparatus that permits saline solution or the like to be drawn into the blood circuit in the circumstance of negative pressure being encountered.
In the prior art, such pillows are made by typically injection molding of a tube having a side port for the branch tube. Then, molded or extruded bushings of smaller diameter are placed into the ends of the tube, so that the central portion of the pillow is of larger diameter, following which the bushings are bonded to the ends of the central tube. This is accomplished by heat sealing the ends of the central tube around the bushings using a well-known type of heat seal.
Such a structure, while having been used through the years, is relatively expensive, requiring the manufacture of precursor parts plus an assembly step involving heat sealing.
Blow molded pillows for medical fluid flow sets are also known in the prior art. In the specific blow molding process, a pillow having an enlarged, tubular central portion and smaller diameter end ports can be blow molded with a lateral, outwardly projecting dimple. After the blow molding step, the dimple is cut open in a further step, and a molded, tubular port is bonded into the cut area where the dimple originally was. Following this, the branch tube can be bonded to the molded port.
This blow molding process for pillows is also cumbersome, multistep, and rather expensive. Also, both of the above manufacturing techniques for pillows for use in flow sets result in pillows which are prone to leaking whenever inadequate seals are formed, and they also often exhibit thrombogenic characteristics because of the presence of sharp, internal corners.
In accordance with this invention, a pillow for a medical fluid flow set is provided in which the whole pillow can be made with a single blow molding step, rather than the multiple assembly steps of the prior art. Furthermore, the blow molded pillow comprises a single, integral piece with all of its respective port tubes, which significantly reduces the risk of leak formation during use of the set in which the pillow is emplaced.
Furthermore, the modifications used in this invention are of a nature that they provide little or no disturbance to other normal procedures of manufacture and use of medical fluid flow sets which include the pillow of this invention. Thus, medical fluid flow sets having the pillow of this invention may still be used with the present commercially available dialyzer units in present, commercially available dialysis machines. Essentially no modification of other equipment is required to accommodate the modified flow set of this invention. Also fewer sharp internal corners are found, for better blood handling.